1. Field of the Invention
The present invention relates to a heat developing apparatus for heating a heat developing photosensitive material or a photosensitive and thermosensitive recording material to perform heat development.
2. Description of the Related Art
As an image recording apparatus for recording an image for medical use in, for example, a digital radiography system, a CT or an MR, a wet system has been used with which an image is photographed or recorded on a silver-salt photosensitive material and after which a wet process is performed to obtain a reproduced image.
On the other hand, a recording apparatus in the form of a dry system with which no wet process is performed has attracted attention in recent years. A recording apparatus of the foregoing type uses a photosensitive and thermosensitive recording material (a photosensitive and thermosensitive recording material) or a heat developing photosensitive material (hereinafter called a xe2x80x9cheat developing recording materialxe2x80x9d). The dry recording apparatus incorporates an exposing portion in which the heat developing recording material is irradiated with a laser beam (that is, scanned) so that a latent image is formed. Then, the heat developing portion brings the heat developing recording material into contact with a heating means so that heat development is performed. Then, the heat developing recording material is cooled, and then the heat developing recording material having an image formed thereon is discharged to the outside of the apparatus.
The heat development performed by the heat developing portion is performed such that the heat developing recording material, the temperature of which is substantially the room temperature, is heated to a level not lower than the heat development start temperature. Then, the temperature is maintained for a predetermined period of time. Hitherto, a heat developing apparatus incorporates a heating means, such as hot air, infrared rays, a heating drum, a heating plate or a heating roller, for heating and developing the heat developing recording material has been known (Japanese Patent Application No. 9-229643).
However, heat conduction in the heat developing portion cannot always uniformly be performed. Therefore, the heat hysteresis differs among the portions of the heat developing recording material. As a result, there is apprehension that irregularity of development occurs. The reason why the heat conduction cannot uniformly be performed has been detected as follows.
The cause of the problem experienced with the conventional apparatus will now be described with reference to FIG. 2.
Referring to FIG. 2, FIG. 2(a) is a diagram showing change in the state of the heat developing recording material placed on a heating plate which is the heating means, the change occurring as time elapses.
FIG. 2(b) is a graph showing change in the temperatures at points A and B of the heat developing recording material occurring as time elapses.
FIG. 2(c) is a diagram showing the sizes (the densities) of recorded dots developed on the points A and B.
Referring to FIG. 2, the heat developing recording material, the temperature of which is the room temperature, is placed on the heater so as to be heated. In a state at time t1 shown in FIG. 2(a), the irregularity of the thickness of the base of the heat developing recording material, that of the density of the material of the base, a state of asperities of the heat developing recording material and irregularity of the heat distribution of the heater causes portions which are intensely heated and portions which are heated weakly to be realized.
As a result, the portions of the heat developing recording material heated intensely (the point A of the heat developing recording material) are quickly heated to the glass transition temperature TG (see FIG. 2(b)). On the other hand, portions of the heat developing recording material heated weakly (the point B of the heat developing recording material) are slowly heated to the glass transition temperature TG.
The portions (the point A) of the heat developing recording material quickly heated to the glass transition temperature lose rigidity quickly. Therefore, the foregoing portions are brought into furthermore hermetic contact with the heater so that greater heat is exerted to the foregoing portions. Therefore, the portions are quickly heated to the development start temperature TH (time t1 shown in FIG. 2(b)). On the other hand, the portions of the heat developing recording material which are heated weakly (the point B) are slowly heated to the glass transition temperature TG. Therefore, the foregoing portions are slowly heated to the development start temperature at time t2 shown in FIGS. 2(a) and (b).
Assuming that the time at which the development of the points A and B is stopped is t4 (see FIG. 2(b)), development time ta at which the point A is developed is expressed by equation (1) and development time tb at which the point B is developed is expressed by equation (2).
xe2x80x83tA=t4xe2x88x92t1xe2x80x83xe2x80x83(1)
tB=t4xe2x88x92t2xe2x80x83xe2x80x83(2)
Since tA and tB satisfy equation (3)
A greater than tBxe2x80x83xe2x80x83(3)
Therefore, the sizes of the recorded dot of the points A and B are as shown in FIG. 2(c). Thus, the point A is formed into a larger dot and has a high density as compared with the point B. Therefore, irregular development takes place over the whole heat developing recording material.
To achieve the foregoing problem, an object of the present invention is to provide a heat developing method with which occurrence of irregularity of heat development can be prevented over the surface of the heat developing recording material and an apparatus therefor.
To solve the above-mentioned problem, according to one aspect of the present invention, there is provided a heat developing method comprising the steps of: initially making the overall surface of a heat developing photosensitive material or a photosensitive and thermosensitive recording material a predetermined temperature not lower than a glass transition temperature and not higher than a heat development start temperature; and performing heat development.
According to another aspect, the method further comprises a step of transferring the heat developing recording material to the heat development wherein said predetermined temperature is slightly lower than a heat developing portion kept at a heat developing temperature.
According to another aspect, heat is independently applied in the widthwise direction of the heat developing recording material.
According to another aspect, the step of heating a plurality of portions comprises the step of heating a portion at the widthwise end that is stronger than other portions of said heat developing recording material.
According to another aspect, there is provided a heat developing apparatus comprising: a heat developing apparatus that includes a recording portion for exposing a heat developing recording material or a photosensitive and thermosensitive recording material (hereinafter called a xe2x80x9cheat developing recording materialxe2x80x9d) to form a latent image; and a heat developing portion for heating said heat developing recording material by a heating medium thereof to perform heat development, wherein
a previously-heating portion for heating the overall surface of said heat developing recording material to a temperature not lower than a glass transition temperature and not higher than heat development start temperature,
a plurality of thermosensors for sampling the temperatures of the overall surface of said heat developing recording material, and
a comparator for performing a comparison whether or not all of the temperatures detected by said thermosensors have been raised to said predetermined temperature are disposed between said recording portion and said heat developing portion, wherein after said comparator has detected that all of the temperatures detected by said thermosensors and said predetermined temperature substantially coincide with one another, said developing operation is started.
According to another aspect, there is provided a heat developing apparatus comprising: a recording portion for exposing a heat developing recording material or a photosensitive and thermosensitive recording material to form a latent image; a heat developing portion for heating the heat developing recording material by a heating medium thereof to perform heat development; and conveying means for conveying the heat developing recording material from the recording portion to the heat developing portion, wherein a previously-heating portion for heating the overall surface of the heat developing recording material to a temperature not lower than a glass transition temperature and not higher than heat development start temperature, a plurality of thermosensors for sampling the temperatures of the overall surface of the heat developing recording material, and a comparator for performing a comparison whether or not all of the temperatures detected by the thermosensors have been raised to the predetermined temperature are disposed between the recording portion and the heat developing portion, and when the comparator has detected that all of the temperatures detected by the thermosensors and the predetermined temperature substantially coincide with one another, the conveying means starts operating.
According to another aspect, the previously heating portion is divided into a plurality of sections in the widthwise direction of the heat developing recording material and controlled such that the temperatures of the sections are independently controlled.
According to another aspect, heating portions of the previously heating portion divided into the plural sections disposed at the two ends of the heat developing recording material in the widthwise direction are controlled to apply greater heat as compared with heating portions disposed in the central portion of the heat developing recording material in the widthwise direction.
According to another aspect, there is provided a heat developing apparatus comprising: a recording portion for exposing a heat developing recording material or a photosensitive and thermosensitive recording material to form a latent image; a heat developing portion for heating the heat developing recording material by a heating medium thereof to perform heat development; and a heating control portion which is capable of controlling the heat of said heat developing portion to two temperature levels including a first heating temperature not lower than a glass transition temperature and not higher than heat development start temperature and a second heating temperature not lower than the heat development start temperature, wherein a plurality of thermosensors disposed in the heat developing portion and arranged to sample the temperatures of the overall surface of the heat developing recording material, and a comparator for performing a comparison between the temperatures detected by the thermosensors and the first heating temperature, and when the comparator has detected that all of the temperatures detected by the thermosensors and the first heating temperature have substantially coincided with one another after an operation for controlling the first heating temperature has been started, the heating control portion issues a command to start a control operation of the second heat temperature.
The heat developing method and the apparatus therefor enable the overall surface of the heat developing recording material to uniformly be made to be the predetermined temperature not lower than a glass transition temperature and not higher than heat development start temperature. Therefore, the overall surface of the heat developing recording material can uniformly contact with the plate heater. Therefore, the overall surface of the heat developing recording material is free from irregularity of the heat development.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.